Deliberately marking bad sectors as "bad" after ddrescue process

New here but hopefully my question will be helpful to others. I'm trying to recover a very old CD. There are total 15 files (out of many, many) that are unreadable by Windows copy. I've used a tool called Roadkil's Unstoppable Copier on 3 of those files, and it successfully reconstructed 2 of them, which is impressive (the 3rd file was really small - 1 Kb - and its corresponding sectors were giving read error as per Unstoppable Copier). Equally impressive is ddrescue which has so far managed to rescue 99.93% of the CD - so that 415774 bytes of bad sector is remaining. I was thinking - hypothetically if the actual physical CD had only 415 Kb of unreadable data (which I'm sure is distributed among those 15 files), then Unstoppable Copier's error correction algorithm would be able to reconstruct those files with much higher probability. Hence my question - suppose there's some bad sectors still remaining after ddrescue's 3 retries, they get filled with zeroes in the resulting .iso file. If I mount that .iso image in a virtual drive and run Unstoppable Copier on it, it won't see the bad sectors as "bad" since they're just zeroes. Is there a way to force those residual sectors to be marked "bad" in the resulting .iso file? So that the Copier can try to reconstruct them based on its error correction algorithm?